Solid electrolytic capacitors of the chip type comprise a capacitor element including a sintered block which has one end of an anode lead embedded therein and which is provided with an insulating layer, electrolyte layer and cathode layer formed over the surface of the block. Common chip-type solid electrolytic capacitors are fabricated by joining a terminal in the form of a thin plate to each of the anode lead and the cathode layer, forming a packaging resin portion around the capacitor element by resin molding and thereafter bending the terminals so as to position the outer ends of the terminals beneath the bottom of the resin portion. However, with a growing demand for compacted chip-type solid electrolytic capacitors of lower ESR, capacitors of such type encounter structural limitations.
JP-A No. 2001-44077 discloses a chip-type solid electrolytic capacitor which is contrived to ensure further compactness and still lower ESR. The disclosed capacitor has an anode terminal extending downward from an anode lead, and a cathode terminal is joined to the bottom surface of a capacitor element (and also to a side surface thereof). Since this type of capacitor has no terminals extending sideways therefrom unlike the conventional solid electrolytic capacitor, the capacitor is compacted, while the capacitor is reduced in ESR because the terminals are shortened.
With reference to FIGS. 9A to 9D, a brief description will be given of a process for fabricating the solid electrolytic capacitor disclosed in JP-A No. 2001-44077. First as shown in FIG. 9A, a plated L-shaped cathode terminal 36 is bonded with an electrically conductive adhesive to a capacitor element 31 having an anode lead 32 secured to a metal ribbon 7. The outer surface of the cathode terminal 36 is masked with an insulator 36a so as not to permit resin to adhere thereto when a packaging resin portion 34 is formed. Next as shown in FIG. 9B, the packaging resin portion 34 for covering the capacitor element 31 is formed thereover by a powder coating machine. The resin portion 34 is so formed as not to cover the outer surface of the cathode terminal 36. As seen in FIG. 9C, the insulator 36a is then removed from the outer surface of the cathode terminal 36. Finally as shown in FIG. 9D, a plated L-shaped anode terminal 35 is joined to the anode lead 32 and to the resin portion 34, and the anode lead 32 is cut to separate the resulting solid electrolytic capacitor from the metal ribbon 7.
The capacitor fabricating process described above is cumbersome because the process includes the step of masking the cathode terminal 35 with the insulator 36a and the step of removing the insulator 36a after the packaging resin portion 34 has been formed. Furthermore, the packaging resin portion 34 can be formed more easily by resin molding as generally practiced in the prior art than by using the powder coating machine. Accordingly, it is desired to fabricate with ease solid electrolytic capacitors of such type that no electrode terminals extend outward and are bent, by a process similar to the prior-art process.
Nevertheless, the following problem is encountered in the case where solid electrolytic capacitors of the type mentioned are fabricated by a process similar to the conventional process. As shown in FIG. 10A, for example, a fabrication frame 1 for use in the process has arranged longitudinally thereof opposed pairs of anode terminal members 12 and cathode terminal members 13 which project inward. The fabrication frame 1 is plated to form a plating layer 23 over the surface thereof, anode leads 32 of capacitor elements 31 are thereafter joined to the respective anode terminal members 12, and the capacitor elements 31 are joined at their bottom surfaces to the respective cathode terminal members 13. A packaging resin portion 34 for covering each of the capacitor elements 31 is formed by resin molding as shown in FIG. 10B.
The anode terminal members 12 and the cathode terminal members 13 are then cut to separate the resulting solid electrolytic capacitors 3 from the fabrication frame 1 as shown in FIG. 10C. The capacitor thus obtained has cut surfaces, i.e., side portions of the anode terminal 35 and the cathode terminal 36, which are not covered with the plating layer 23 (which is formed only at edges of the side portions), so that these side portions must be plated after the cutting step. The reason is that major areas of side surfaces of the anode terminal 35 and the cathode terminal 36 to which solder adheres when the capacitor is mounted on a board need to be covered with a plating layer so as to ensure an enhanced bond strength. However, performing the plating step twice in fabricating the solid electrolytic capacitor is inefficient, while plating the capacitors individually after the separating step is extremely cumbersome. It is therefore desired that the plating step to be performed during the fabrication of solid electrolytic capacitor be limited to that for the fabrication frame 1.
The present invention has overcome the above problem and provides a process for fabricating a solid electrolytic capacitor of the type having no electrode terminals extending outward and bent which process includes a simplified plating step. The invention further provides the capacitor which is fabricated by this process and which can be soldered to a board rapidly with safety.